Dinuclear lanthanide(III) complexes from the use of di-2-pyridyl ketone: Preparation, structural characterization and spectroscopic studies
The use of di-2-pyridyl ketone ((py)2CO) in lanthanide(III) chemistry has yielded neutral dinuclear complexes. The 1:1:1 Ln(NO3)3 ΖxH2O/(py)2CO/LiOH ΖH2O reaction mixtures in MeOH–EtOH afford the complexes [Ln2(NO3)3{(py)2C(OMe)O}2{(py)2- C(OH)O}] (Ln = Pr, 1; Ln = Eu, 2; Ln = Tb, 3; Ln = Er, 4).
The monoanionic derivatives of the hemiacetal and the gem-diol forms of di-2-pyridyl ketone have been derived from the Ln(III)-mediated addition of solvent (MeOH, H2O involved in the alcohols and in the starting materials) on the carbonyl group of (py)2CO. The crystal structure of the representative complex 4 Ζ0.8EtOH Ζ0.4MeOH has been solved by single-crystal X-ray crystallography. The two ErIII atoms are doubly bridged by the deprotonated oxygen atoms of the g1:g2:g1:l2 (py)2C(OH)O_ ligand and one g1:g2:g1:l2 (py)2C(OMe)O_ ion. One ErIII atom is in a nine-coordinate tricapped trigonal prismatic ligand environment comprising the two bridging hydroxyl oxygen atoms, four oxygen atoms from two chelating nitrato ligands and three 2-pyridyl nitrogen atoms, while dodecahedral, eight-coordination at the other ErIII atom is completed by two oxygen atoms of the third chelating nitrato ligand, one nitrogen atom of the bridging (py)2C(OMe)O_ ligand and the N,N,Odeprotonated triad from one tridentate chelating (py)2C(Me)O_ ion. The complexes were characterized by room-temperature effective magnetic moments and spectroscopic (IR, solid-state f–f) techniques. All data are discussed in terms of the nature of bonding and known (4) or assigned (1–3) structures. The Eu(III) and Tb(III) complexes 2 and 3 display in the solid state and at room temperature an intense red and green emission, respectively; this photoluminescence is achieved by an indirect process (antenna effect).